The 18Z GFS is very similar to the 12Z GFS through 120 hours... though stalling Wilma right on the Yucutan coast compared to stalling it further inland. It is about 6 hours faster in bringing the system into the Keys and S. Florida by Sunday evening. While the 18Z models will be what NHC has to go on for the 11pm forecast update, the real crucial model data will be the 00Z model runs, which will have another set of radiosonde data to ingest. There is typically a lot more new data to ingest at 00Z and 12Z than at 06Z and 18Z, for those who are unfamiliar.